MTb (Mycobacterium tuberculosis) drives enhanced HIV replication and disease progression and, conversely, HIV-induced CD4+ T cell depletion increases risk of de novo MTb infection and, more importantly, MTb reactivation from latency. Alveolar macrophages (AMs) are a primary target of MTb upon transmission and are also a major source of slowly replicating and/or dormant mycobacterial in granulomous lesions. AMs are also infected by HIV acutely and harbor latent HIV. MTb replication within AMs also drives local inflammation in the lung, which in can in turn drive HIV reactivation from latency. Thus, improved understanding of the immunological and cellular mechanisms involved in the control of latent and active TB in the context of HIV infection in macrophages is critical for the design of novel treatments aimed at controlling co-infection and expediting the clearance of latent organisms to reduce risk of MTb reactivation. Our preliminary studies have demonstrated that an interferon-stimulated gene (ISG) product, interferon-inducible trans-membrane protein 3 (IFITM3), is induced by MTb infection and inhibits MTb and HIV-1 infection of human monocytes and monocyte -derived-macrophages (MDM). We have also found that the FDA-approved small molecule nitazoxanide (NTZ) induces expression of IFITM3 and also induces the HIV restriction factor SAMHD1. Furthermore, we have shown that NTZ inhibits MTb and HIV infection in monocytes and MDM, and suppresses MTb- and TLR- mediated activation of a silent mini HIV-1 provirus in monocytic cells. Based on our preliminary data, we will test the major hypothesis that (i) IFITM3 is a criticl immune modulator that inhibits MTb/HIV-1 co-infection and MTb survival in target cells of the lung, and (ii) that NTZ inhibits growth of both pathogens through direct stimulation of IFITM3, as well as additional host factors including PKR and, in the case of HIV-1 specifically, SAMHD1. Specifically, in Aim 1 we will test the hypotheses that IFITM3 is a critical immune modulator of TB/HIV co-infection, and that it restricts MTb infection via perturbation of host lipid biosynthesi and localization to the maturing phagosome. In Aim 2 we will focus on elucidating the mechanisms involved in NTZ inhibition of MTb and HIV infection of myeloid cells. We will test the hypothesis that NTZ inhibits MTb via its induction of IFITM3 and PKR, and that it inhibits HIV infection via its induction/activation of SAMHD1 and PKR. Furthermore, we will investigate whether NTZ's inhibitory effect upon HIV and TB involves stimulation of PKR- dependent autophagy, leading to enhanced viral and bacterial degradation. We expect to identify novel IFITM3-associated mechanisms of dual TB/HIV suppression, including those that are critical for MTb survival and metabolic switching to dormancy that will serve as attractive targets for simultaneous modulation of both latent and active TB disease in the context of HIV co-infection. We also anticipate that we will identify molecular and immunological correlates of NTZ-mediated anti-TB/HIV activity that will provide a foundation for the rapid repurposing of NTZ as a treatment of latent TB and TB/HIV.